The Iraqi president predicted yesterday that Iraqi troops could replace British soldiers in the country by the end of next year, in what is the most optimistic assessment yet of the ability of his own forces to take responsibility for the security of the country.

Jalal Talabani, the Kurdish leader running for re-election next month, said: "We don't want British forces forever in Iraq. Within one year, I think at the end of 2006, Iraqi troops will be ready to replace British forces in the south."

General Sir Mike Jackson, the head of the army, said Mr Talabani's prediction of a British departure by the end of 2006 was "well within the range of what is realistically possible". However, a senior British defence source, speaking on condition he would not be named, described the president's remarks as being made "more in hope than expectation".

John Reid, the defence secretary, was also more cautious. He insisted: "We will stay in Iraq until the job is done." But he added: "That job will be done when the Iraqis themselves are capable of taking their own security into their own hands, and that handover is something that could begin in parts of Iraq in the course of the next year."

Privately, British and American commanders in Iraq are concerned about the lack of progress in building up a national Iraqi security and police force, a problem compounded by the infiltration of the Iraqi police by Shia militia in British-controlled southern Iraq.

The US president, George Bush, has refused to set a timetable for withdrawing 150,000 American troops from the country, saying it would play into the hands of insurgents. However, Iraq's deputy prime minister, Ahmad Chalabi, said on Friday that US troops could begin leaving in significant numbers sometime next year.

Asked on ITV1's Jonathan Dimbleby programme whether his assessment amounted to a commitment, Mr Talabani replied: "Well, I haven't been in negotiations, but in my opinion and according to my study of the situation I can say that it is the just estimation of the situation ... There is not one Iraqi that wants that forever the troops remain in the country."

Mr Talabani said he understood that the British people were eager for their troops, who currently number 8,500, to return home. "British people have full right to ask this, their sons coming back home, especially if they have finished their main job, which was the ending of dictatorship," he said.

But immediate withdrawal would be a "catastrophe" and lead to a kind of civil war, he said. "We will lose what we have done for liberating Iraq from worst kind of dictatorship ... Instead of having a democratic, stable Iraq, we will have a civil war in Iraq, we will have troubles in Iraq [and they] will affect all the Middle East."

Mr Talabani called for a gradual pull-out, with close coordination between coalition nations and the Iraqi authorities. He acknowledged that an upsurge of violence could be expected in the run-up to the national assembly elections on December 15, but denied that insurgents would have an impact on the result.

Asked about fears that the security forces had been infiltrated, he said: "It is the fault of some generals who started to organise the police force at the beginning.

General Jackson, interviewed on BBC1's Sunday AM programme, said it was important not to set a timetable for withdrawal at this point."What we are trying to achieve are a set of conditions at which point we have the confidence - and more importantly the Iraqi government and Iraqi people have the confidence - that they can fully stand on their own feet and there is no requirement to be supported by the coalition.

"When these conditions come together, then the time will be right," he said. "The president [Talabani] has said we could leave within a year, and I would agree we certainly could, but it is a question of achieving the right conditions."

He was "quite encouraged" by a visit last month to Iraq, where he had found the political progress "in some ways quite remarkable". He conceded that the security situation was "rather less than anyone would wish", but added that violence was largely confined to four of Iraq's 18 provinces. There was "reason to conclude that there is some Iranian influence in what is going on in Iraq, and perhaps in particular the south of Iraq", he said.

But he made it clear he did not know whether the Tehran government was behind cross-border activity. Intelligence officials believe that Iranian revolutionary guards or Hizbullah guerrillas may have supplied explosive devices used against British troops in southern Iraq.